1. Field of the Invention
The present general inventive concept relates to a hard disk drive, a method of controlling the flying height of a magnetic head of the hard disk drive, and a recording medium recording a computer program executing the method, and more particularly, to a hard disk drive which can actively control the flying height of a magnetic head, a method of controlling the flying height of a magnetic head of the hard disk drive, and a recording medium recording a computer program executing the method.
2. Description of the Related Art
Hard disk drives (HDDs) formed of electronic parts and mechanical parts are one of memory devices for recording and reproducing data by converting digital electric pulses to a magnetic field that is more permanent. The HDD is widely used as one of auxiliary memory devices for a computer system because of its fast access time to a large amount of data.
With the recent increase in TPI (tracks per inch) and BPI (bits per inch), the HDD has achieved a high storage capacity and its application field has expanded. As the storage capacity of the HDD continues to increase, the size of a read/write sensor of a magnetic head decreases and a flying height FH of the magnetic head flying above a recording surface of a disk gradually decreases. That is, when high TPI and BPI are embodied to manufacture an HDD with a high storage capacity, the width of a track decreases, and accordingly the strength of a magnetic field decreases in proportional thereto. Thus, when the FH of a magnetic head increases, the detection of a magnetic head is difficult so that the operation of the HDD is not smooth.
In this regard, a study on a method of effectively reducing the FH of a magnetic head with respect to a disk by appropriately controlling the FH of the magnetic head is widely performed and one of the methods is the flying on demand (FOD) method. The FOD is a method of controlling the FH of a magnetic head using a reduction characteristic of the FH of a magnetic head generated during thermal expansion of a pole tip that is an end portion of the magnetic head, during the operation of the HDD, by applying a constant voltage, that is, an FOD voltage, to a heater coil included in the magnetic head.
Recently, a reference FOD voltage (or an FOD current or FOD power) profile indicating a relationship between the FH of a magnetic head and an FOD voltage is calculated using an FOD apparatus in a burn-in process. The FOD voltage is selected to maintain a desired FH of a magnetic head in a user's environment based on the reference FOD voltage profile. In detail, in the burn-in process, when a gradually increasing FOD voltage is applied to the magnetic head through a touch down test, the magnetic head maintaining a flying state at a predetermined height is gradually lowered toward the disk and is finally touched down on the disk. The reference FOD voltage profile indicating the relationship between the FOD voltage and the FH of the magnetic head is provided through the touch down test.
A target clearance, that is, an FOD voltage needed for a target FH, in an actual user environment is calculated from the reference FOD voltage profile, and related data is stored in a maintenance cylinder of a disk. Thus, the FOD voltage calculated in the burn-in process is applied to the heater included in the magnetic head in the user environment so that a target FH of the magnetic head is maintained.
However, environments where the HDD is actually used are quite various so as not to be the same as the environment of the burn-in process. Accordingly, when the FOD voltage needed for a target FH, which is selected based on the reference FOD voltage profile provided in the burn-in process, as described above, is applied to the user environment where the HDD is actually in use, the FH of the magnetic head may vary according to the environment where the HDD is used. In particular, since a temperature sensor is generally included in the HDD, even when the effect by a temperature is compensated for to a degree by measuring a change in the temperature using the temperature sensor, it is very difficult to reflect a change in the altitude or humidity, or other environmental factors that affect the FH of the magnetic head.
When the HDD is used in the user environment based on the FOD voltage measured in the burn-in process, the target FH of the magnetic head may not be maintained due to an effect of a combination of various environment variables. When the target FH of the magnetic head is not maintained, a problem of weak write or head/disk interference (HDI) can be generated so that the reliability of FOD is deteriorated.
Thus, since the target FH of the magnetic head cannot be maintained with the FOD voltage selected based on the touch down test in the burn-in process due to complex issues of various environment variables, there is a demand to appropriately address these and other related problems.